FENSA Certificates Explained: Why They Matter

The short answer

FENSA (Fenestration Self-Assessment Scheme) is the UK's main competent person scheme for replacement windows and doors. Using a FENSA-registered installer means the work is self-certified as complying with Building Regulations, and you receive a FENSA certificate as proof — without it, you'd need to arrange separate Building Regulations sign-off from your local council, which costs more and takes longer.

Why replacing windows or doors needs Building Regulations sign-off at all

Since 2002, replacing windows, doors or roof windows in England and Wales has been "controlled work" under Building Regulations — mainly around thermal performance (the new installation must meet current energy efficiency standards) and, where relevant, safety glazing and means of escape. This applies whether you're replacing a single window or doing a whole-house upgrade. It's easy to assume this only applies to bigger structural work, but a straightforward like-for-like window replacement is still covered.

What FENSA registration actually means

A FENSA-registered installer has been assessed and is authorised to self-certify that their installation work complies with the relevant Building Regulations, without needing your local council's Building Control department to inspect it separately. After the work, FENSA notifies your local authority on the installer's behalf and issues you a certificate, which becomes an important document — you'll typically need to produce it when selling your home, since conveyancing solicitors routinely ask for proof that window/door replacements had proper Building Regulations sign-off.

What happens if your installer isn't FENSA-registered

You can still use a non-registered installer, but the work then needs to be separately notified to, and inspected by, your local council's Building Control department — an additional process with its own fee (commonly £150–£350+, varying by council), and one that's easy to overlook until you come to sell the property and can't produce evidence the work was compliant. Retrospectively regularising unauthorised building work is more expensive and slower than getting it right at the time, so checking FENSA registration (or an equivalent competent person scheme, such as CERTASS or the British Fenestration Rating Council) before booking an installer is a genuinely worthwhile five-minute check.

How to check an installer is FENSA-registered

FENSA maintains a searchable installer database on its own website — search by company name or postcode to confirm current registration before booking, since registration can lapse. Don't rely solely on a logo on a van or a claim in a quote; verifying against the official register takes a couple of minutes and avoids any doubt.

What the certificate covers — and doesn't

A FENSA certificate confirms the installation met Building Regulations at the time of work — primarily thermal performance and safety glazing requirements. It isn't a general guarantee of workmanship quality or a warranty against the product failing years later; that's a separate matter covered by the manufacturer's product warranty and the installer's own workmanship guarantee, which are worth checking and keeping paperwork for separately.

When you're selling a property without a certificate

If you're selling and can't locate FENSA certificates for windows or doors replaced during your ownership (or a previous owner's), options include applying to FENSA for a retrospective certificate if the installer is still registered and the records exist, applying to your local council for retrospective Building Regulations approval (an inspection-based process, with a fee), or taking out indemnity insurance to cover the risk — a route some buyers' solicitors will accept, though not universally. Sorting this before marketing the property avoids delays during a sale.

Common mistakes

• Assuming a small window replacement doesn't count as "building work." It does, under Building Regulations, regardless of scale.
• Not keeping the certificate somewhere safe. Store it with other property paperwork — you may not need it for years, but you will need it eventually.
• Choosing an installer on price alone without checking registration. An unregistered installer's quote might look cheaper, but factor in the separate Building Control fee and hassle you'd otherwise need to arrange yourself.

The bottom line

Whether you're weighing up window materials, a new front door, or bifold doors, checking your installer's FENSA registration before booking is one of the simplest ways to avoid paperwork problems down the line — and it costs nothing to check.